This invention relates to devices for detecting pollutants and more particularly to devices capable of detecting pollutants at relatively low concentrations in ambient gases. Electrochemical sensing devices, especially amperometric sensors such as those disclosed in U.S. Pat. Nos. 3,776,832, 4,201,634 and 4,326,927 offer the advantages of portability, real-time readout, relatively low cost, and fair sensitivity and selectivity to a few specific pollutants such as CO, H.sub.2 S, NO, NO.sub.2, SO.sub.2, hydrazine, COCl.sub.2, HCN, or Cl.sub.2. However, these devices are not applicable, at present, to the detection of many species that are not electrochemically active.
In detecting pollutants including toxic substances, sensing devices have usually been limited with respect to concentrations of the pollutants particularly when the pollutants are essentially not electrochemically active or have an activity difficult to detect. Below certain values of concentration, e.g., 100 ppm (parts per million) of benzyl chloride, tetrachloroethylene or the like, presently available portable devices are essentially unresponsive to the pollutant. Since some pollutants may be extremely toxic, it is important to develop devices for detecting various pollutants at low concentrations.
Accordingly, one object of this invention is a device for detecting pollutants at low concentrations in gases. Another object is an electrochemical device for detecting pollutants in ambient gases where the pollutants are essentially electrochemically inactive or have an activity difficult to detect. An additional object is a device which may be utilized as a portable instrument to survey an area or as a site monitor for a wide variety of gases. A further object is a device which is also capable of detecting pollutants at higher concentrations, at which level they may present an acute toxicity or flammability hazard.